Carrier mobility of a transistor is often increased when a strain is applied to the channel of the transistor. For example, in a p-type transistor, the application of a compressive longitudinal strain to the channel usually increases the drive current of the p-type transistor. Silicon germanium is a desirable lattice-mismatched semiconductor for use in forming strained channels in silicon-based p-type transistors, because silicon germanium has a larger lattice constant than silicon and a compressive strain is often created in silicon germanium when silicon germanium grows epitaxially on silicon. However, if the germanium concentration in a silicon germanium channel on silicon exceeds a certain threshold (e.g., 30%), a relaxed graded buffer is often needed to reduce defects in the silicon germanium channel caused by the lattice mismatch between silicon germanium and silicon.